British soldiers were guarding the scene of a suicide bombing outside the Afghan capital Kabul which has killed up to 10 people, including Nato staff.
Dozens more were injured in the attack on a convoy near a military base which came two days before national elections to select a new president.
The Taliban claimed responsibility for the attack.
A Nato spokeswoman confirmed the attack involved the alliance's vehicles. She said there were "some casualties" and several troops were wounded.
The International Security Assistance Force in Afghanistan (Isaf) said reports indicated both Afghan civilians and Isaf service members were killed and wounded in the blast.
The suicide attack was on the road leading from Kabul to Bagram Air Base, the largest facility in the country. The Taliban has denounced the election and warned people they would be at risk if they attend polling stations.
Colonel Wayne Shanks, an Isaf spokesman, said: "This is yet another indiscriminate attack on both the people of Afghanistan and our forces who are working with our Afghan partners to protect them.
"I want to express our sincere condolences to the families for their loss, but these words are not adequate to capture the loss of any service member or civilian and the grief their families must be experiencing.
"However, we will not let this attack weaken our determination to bring security to the Afghan people and allow them the right to vote. We will work with the Afghan authorities to bring those responsible to justice for this disgraceful crime."
The UK provides a small number of service personnel in support of Isaf's headquarters, in Kabul. There was no early indication what nationality Isaf casualties might be.
